1. Field of the Invention
The present invention relates to a low pass filter having an attenuation pole near a pass band, and to a wave splitter including the low pass filter.
2. Description of the Related Art
Hitherto, an example of this type of low pass filter (hereinafter also referred to as an “LPF”) is an LPF disclosed in Japanese Unexamined Patent Application Publication No. 2010-232765. This LPF includes a series arm and three parallel arms, which are first through third parallel arms. Two parallel resonance circuits, for example, are disposed on this series arm. The first parallel arm is disposed between an input terminal of the LPF and the preceding parallel resonance circuit. The second parallel arm is disposed between the two parallel resonance circuits. The third parallel arm is disposed between the subsequent parallel resonance circuit and an output terminal of the LPF. A capacitor is disposed on each of the first through third parallel arms.
Japanese Unexamined Patent Application Publication No. 2010-232765 does not disclose a specific arrangement of inductors and capacitors. However, Japanese Unexamined Patent Application Publication No. 6-176966 discloses an arrangement of inductors and capacitors of a filter (hereinafter such a filter may also be referred to as an “LC filter”), although this filter is not an LPF. In this LC filter, at least one capacitor (that is, an internal capacitor) defined by a plurality of inner electrodes is disposed within a dielectric substrate. On the top surface of the dielectric substrate, two chip coils and two capacitors (that is, external capacitors) are mounted. The internal capacitor, the chip coils, and the external capacitors are electrically connected to one another, thereby forming an LC filter. The chip coils, which are of a vertical-winding type, are mounted on the top surface of the dielectric substrate such that the axis of a core of each of the chip coils is substantially perpendicular to the top surface of the dielectric substrate. Accordingly, the axes of the chip coils are substantially parallel with each other. Concerning the arrangement of the chip coils, one of the chip coils is disposed at a corner of the dielectric substrate, while the other chip coil is disposed at another corner of the dielectric substrate, thereby providing a large distance between the chip coils. The chip coils are arranged in this manner in order to reduce the influence of magnetic coupling between the chip coils. As a result, the characteristics of the LC filter can be maintained.
However, on the other hand, with the arrangement of the chip coils used in this publication, it is necessary to provide a large distance between the chip coils, thereby making it difficult to reduce the size of the LPF.